This invention relates to blood sampling devices.
A common form of blood sampling device is a skin pricker comprising a spring loaded lancet in a small plastics housing with a trigger mechanism to release the lancet. Some require the lancet to be cocked or primed before being released, while others are assembled and sold in the cocked condition, ready to fire. But they are all quite simple and cheap, and can be thrown away after a single use.
A standard feature is that the lancet springs back a sufficient distance to retract the needle tip inside the housing after that tip has momentarily projected. Whilst that can give protection against subsequent injury, various measures have been devised to try to ensure that the user cannot reset the device and fire it again. This has certainly been made difficult, but the ideal is to make it impossible.
One solution to this has been proposed in EP-B-0 582 226, where the lancet has wings that initially rest against internal shoulders of the firing device, holding the lancet back against a drive spring. A push button at the rear end is pressed to force the wings to break off or fold back, allowing the drive spring to act and urge the lancet forwards. If the wings fold, as shown in FIG. 2 of the Patent, they will drag against the inside of the barrel of the firing device and impede retraction. In any event it is deemed necessary to provide a return spring. Also, the push button action and the radially projecting wings combine to require the rear end of the barrel to be rather bulky, first to provide the internal shoulders and secondly to provide external shoulders affording a grip for the user against the forward pressure of the push button. So it is not particularly compact and it requires a considerable number of components (barrel, two springs, push button and lancet) to be assembled.
It is the aim of this invention to provide a sleeker, non-reusable device with fewer components.
According to the present invention there is provided a blood sampling device comprising a barrel containing a spring-loaded lancet releasable by a trigger from a primed rearward position, momentarily to project its tip from the forward end of the barrel, the lancet having a distortable or detachable appendage to engage the barrel and hold the lancet against a drive spring, characterised in that the appendage extends rearwardly from the lancet and latches to a detent provided by the internal structure of the barrel, and in that the release of the lancet is by a trigger integral with the barrel being pressed in transversely to the barrel to unlatch the appendage.
Conveniently, the housing is an integral moulding with two halves hinged together to encase the lancet and a spring. Preferably, the trigger is an elongate element springing outwardly and rearwardly from one half of the barrel and with a rear end portion capable of projecting in through an aperture in the barrel to co-operate with the appendage. When actuated, the trigger may have a snap engagement with the barrel to retain it in its actuated position. This serves both as an indication that the device has been used and as a back-up for the non-recocking feature.
The appendage may have resilient flexure so that, after clearing the detent and trigger, it resumes its original position and will engage a portion of the retained trigger forward of the detent if the lancet is urged back towards its primed position. In the absence of any prior obstruction by the trigger, the latch can engage the forward side of the detent. Alternatively the appendage may have a weakness at its root causing it to stay bent after clearing the detent, so that if the lancet is urged back to its primed position, the appendage will not re-latch to the detent.
The detent is conveniently formed by two transverse webs which, when the halves are brought together, form an aperture through which the appendage extends. A finger may then project back parallel to the appendage from the rear end of the lancet and engage the edge of the aperture remote from the trigger, thereby ensuring that, when the trigger is pressed in, the lancet is maintained in its proper alignment.
In an alternative arrangement the rear end of the appendage has a narrow neck and a head which engages behind the detent over which the neck lies, and the trigger has a portion formed as a blade which initially registers with the neck and, when the trigger is pressed in, severs the neck to cause the head to fall free and the lancet to be sprung forwards.
The spring will generally be a helical spring that surrounds and is connected to the lancet, acts between the forward end thereof and an abutment forward of the detent, and extends beyond its relaxed state when driving the lancet forwards so that it withdraws the lancet tip into the barrel after the momentary projection. It is thus well clear of the part of the lancet that co-operates with the detent and does not will not interfere with the latching arrangement.